No I haven't heard or seen any of such site's and it would be absolute madness if a site implements this. How in the world would they make profit? They would end up in looses, plus if one user does not pay, the site would be termed as a scam, so no that's a stupid idea and I would not bet with such sites as this are not trust worthy to me, would recommend you to stay away from such sites or methods as it won't have good results.